It is well known that the taste of a variety of foods is degraded under the effect of oxidation by oxygen present in the air. For this reason, when various foods are distributed or stored, they are typically sealed in metal cans or glass bottles which are impermeable to oxygen or in resin containers which have low oxygen permeability. Furthermore, an antioxidant such as ethylenediamine tetraacetic acid (EDTA) or vitamin E is often introduced into the foods. However, this is not desirable, since consumers tend to avoid using the antioxidant. A technique was developed for reducing the amount of dissolved oxygen in starting materials or preventing the penetration of oxygen during manufacture of various foods. For example, Japanese Patent Application Laid-open No. H6-141776 disclosed a technique for obtaining high-quality coffee beverages by extracting coffee substantially without oxygen. Furthermore, Japanese Patent Application Laid-open No. H10-295341 disclosed a technique for obtaining products with good taste by conducting heat treatment of milk beverages or juices under conditions such that the dissolved oxygen concentration is reduced to 5 ppm or less.
Furthermore, Kohyo (Japanese translation of a PCT application) Publication No. H11-504963 described a technique for removing oxygen dissolved in a salad dressing by using a special enzyme as a technique for removing dissolved oxygen present in oil-in-water type emulsified foods such as salad dressings.
However, many of oil-in-water type emulsified foods, for example mayonnaise, have a high viscosity or contain a large amount of solid ingredients, like tartar sauce. For this reason, the active removal of the dissolved oxygen present in the product during manufacture thereof is generally not conducted because such a procedure greatly increases the production cost, for example, because of complex equipment involved. Therefore, with typical commercial oil-in-water type emulsified foods, only measures aimed at preventing the penetration of oxygen into the finished foods were implemented, those measures including preparing and transporting the starting materials in a sealed production line so as to minimize the penetration of oxygen present in the air into the foods, replacing the head space in containers with nitrogen when the containers are filled with the food, and employing glass bottles and jars which are absolutely impermeable to oxygen or resin multilayer bottle containers with reduced oxygen permeability as containers which are to be filled with the products and sealed.
For this reason, the dissolved oxygen concentration immediately after the production of the commonly, commercially available oil-in-water type emulsified foods is at a comparatively high level of 10 to 15% O2.
With the foregoing in view, the inventors have conducted a study aimed at the development of oil-in-water type emulsified foods of higher quality, this study being focused on active removal of dissolved oxygen present in the starting materials and the food in the process for the manufacture of container-packed, oil-in-water type emulsified food products. Initially, the inventors assumed that if the dissolved oxygen present in oil-in-water emulsified foods is completely removed, then the oxidation of edible oils and fats and various spices and seasoning components can be prevented and container-packed, oil-in-water type emulsified food products that have excellent taste can be produced. However, the results of the study demonstrated that excessively removing the dissolved oxygen present in the oil-in-water type emulsified foods surprisingly adversely affects the taste of the oil-in-water type emulsified foods. Thus, if the dissolved oxygen present in the oil-in-water type emulsified foods is removed in excess, a strong pungent irritating odor of vinegar can be noted, matching of flavors of the edible oils and fats, vinegar, and egg yolk is degraded, and flavor balance is lost.
Thus, it is an object of the present invention to provide an container-packed, oil-in-water type emulsified food product, in which excess oxidation of the oil-in-water type emulsified food in storage is prevented, quality degradation is avoided, and excellent flavor balance is obtained by reducing the amount of dissolved oxygen present in the container-packed, oil-in-water type emulsified food and adjusting it to optimum concentration.